CONTRIBUTORS

--- a/CONTRIBUTORS	Fri Jan 08 20:40:56 2021 +0100
+++ b/CONTRIBUTORS	Fri Jan 08 19:53:44 2021 +0100
@@ -6,6 +6,12 @@
 Contributions to Isabelle2021
 -----------------------------
 
+* January 2021: Manuel Eberl
+  Characteristic of a semiring
+
+* January 2021: Manuel Eberl
+  Algebraic integers in HOL-Computational_Algebra
+
 * December 2020: Stepan Holub
   Contributed lemmas for theory HOL.List.